Therapeutic agents can be delivered orally, transdermally, by inhalation, by injection or by depot with slow release. However, the method of delivery is limited by the processing that the agent is subjected to in the recipient, by the requirement for frequent administration, and limitations on the size of molecules that can be utilized. For some of the methods, the amount of therapeutic agent varies between administrations.
Protein production techniques which involve the sub-cloning of a desired nucleic acid sequence/fragment into a vector which is subsequently used for modifying specific host cells, which are meant to produce the desired protein for further purification steps are limited in the amount of protein expressed, protein secretion, post-translational modifications (such as glycosylation and the accurate folding of the protein), etc. Moreover, even if a high-level of protein production could be achieved, large quantities of the recombinant protein must then be produced and purified to be free of contaminants. Development of a purification scheme is a very lengthy process. And once purified recombinant protein has been obtained, it must be further formulated to render it stable and acceptable for introduction into animals or humans. Furthermore, even formulated, purified recombinant proteins have a finite shelf life due to maintenance and storage limitations; often requiring repeated purification and formulation of more protein. The process of developing an appropriate formulation is time consuming, difficult, and costly, as well.
Thus, there is a widely recognized need for long-lasting protein-based therapeutic molecules that have the requisite post-translational modifications to preserve their biological activity, which are produced inexpensively and quickly without the need for the laborious and costly methods typically associated with obtaining high-levels of recombinant proteins.
Some researchers have attempted to obtain in vivo expression of recombinant gene products via gene therapy. Typically viral vectors are used to transduce cells in vivo to express recombinant gene products. These viral-based vectors have advantageous characteristics, such as the natural ability to infect the target tissue. However, retrovirus-based vectors require integration within the genome of the target tissue to allow for recombinant product expression (with the potential to activate resident oncogenes) and can only be used to transduce actively dividing tissues. Viral vectors are also often not able to sustain long-term transgene expression, which may be due at least in part to their elimination due to secondary host immune responses.
Accordingly, there remains a need in the art for recombinant gene product formulations that have consistently high expression levels lasting for several weeks or more and for methods of using those formulations to treat disease.